1. Field of the Invention
The present invention relates to a carrier-driving device mainly used for such a system as a video-projection system and television system, and more particularly to a carrier-driving device in which a carrier member bears a projector mirror adapted to the system.
2. Description of Related Art
Such a carrier-driving device includes supporting arm assemblies for supporting the carrier member and telescopically transporting it in a direction upwardly inclined to a horizontal direction. One goal in this case is to transport the carrier member when carrying a heavy load only by means of driving cables. Such cable should be provided with sufficient hardness in order to bear the load applied to the supporting arm without its bending, with necessary flexibility in order to be sufficiently engageable with a driving wheel and a diametrical size restricted in order to be inserted into the hollow portions of the supporting arms.
Furthermore, a driving wheel should preferably be controllable by manual operation, when it is necessary, such as when the driving motor becomes disabled.
In order to maintain safe operation, when an overload condition occurs on the supporting arm, the driving wheel made be made capable of being separated from the driving source, for instance, from a driving electric motor, when overloaded. Also, the electric motor may be controlled to be automatically stopped upon detection of this overload condition.
It is an object of the invention to provide a carrier-driving device which meets the above specifications.